For a bearing where average of outer diameter of bearing and diameter of axle hole is 50 mm, and that is rotating at 3000 RPM, recommended dynamic viscosity is 12 mm2/s.[7]

The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit the loads through the balls. In most applications, one race is stationary and the other is attached to the rotating assembly (e.g., a hub or shaft). As one of the bearing races rotates it causes the balls to rotate as well. Because the balls are rolling, they have a much lower coefficient of friction than if two flat surfaces were sliding against each other.

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Bearings have static load ratings. These are based on not exceeding a certain amount of plastic deformation in the raceway. These ratings may be exceeded by a large amount for certain applications.

In general, ball bearings are used in most applications that involve moving parts. Some of these applications have specific features and requirements:

Most bearings are meant for supporting loads perpendicular to axle ("radial loads"). Whether they can also bear axial loads, and if so, how much, depends on the type of bearing. Thrust bearings (commonly found on lazy susans) are specifically designed for axial loads.[7]

A sideways torque on a radial bearing also applies pressure to the cage that holds the rolling elements at equal distances, due to the rolling elements trying to all slide together at the location of highest sideways torque. If the cage collapses or breaks apart, the rolling elements group together, the inner ring loses support, and may pop out of the center.

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Note that dynamic viscosity of oil varies strongly with temperature: a temperature increase of 50–70 °C causes the viscosity to decrease by factor 10.[7]

If both axial and radial loads are present, they can be added vectorially, to result in the total load on bearing, which in combination with nominal maximum load can be used to predict lifespan.[7] However, in order to correctly predict the rating life of ball bearings the ISO/TS 16281 should be used with the help of a calculation software.

For single-row edge-contact ball bearings, axial load can be about 2 times max radial load, and for cone-bearings maximum axial load is between 1 and 2 times maximum radial load.[7]

If a bearing is rotating, but experiences heavy load that lasts shorter than one revolution, static max load must be used in computations, since the bearing does not rotate during the maximum load.[7]

If a bearing is not rotating, maximum load is determined by force that causes plastic deformation of elements or raceways. The indentations caused by the elements can concentrate stresses and generate cracks at the components. Maximum load for not or very slowly rotating bearings is called "static" maximum load.[7]

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The ball size increases as the series increases, for any given inner diameter or outer diameter (not both). The larger the ball the greater the load carrying capacity. Series 200 and 300 are the most common.[4]

A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.

Also, if a bearing is not rotating, oscillating forces on the bearing can cause impact damage to the bearing race or the rolling elements, known as brinelling. A second lesser form called false brinelling occurs if the bearing only rotates across a short arc and pushes lubricant out away from the rolling elements.

If the bearing is used under oscillation, oil lubrication should be preferred.[8] If grease lubrication is necessary, the composition should be adapted to the parameters that occur. Greases with a high bleeding rate and low base oil viscosity should be preferred if possible.[9]

If a sideways torque is applied to a deep groove radial bearing, an uneven force in the shape of an ellipse is applied on the outer ring by the rolling elements, concentrating in two regions on opposite sides of the outer ring. If the outer ring is not strong enough, or if it is not sufficiently braced by the supporting structure, the outer ring will deform into an oval shape from the sideways torque stress, until the gap is large enough for the rolling elements to escape. The inner ring then pops out and the bearing structurally collapses.

Bearingmanufacturing process PDF

Lubrication can also be done with an oil, which has advantage of higher maximum load, but needs some way to keep oil in bearing, as it normally tends to run out of it. For oil lubrication it is recommended that for applications where oil does not become warmer than 50 °C, oil should be replaced once a year, while for applications where oil does not become warmer than 100 °C, oil should be replaced 4 times per year. For car engines, oil becomes 100 °C but the engine has an oil filter to maintain oil quality; therefore, the oil is usually changed less frequently than the oil in bearings.[7]

The recommended dynamic viscosity decreases with rotating frequency. As a rough indication: for less than 3000 RPM, recommended viscosity increases with factor 6 for a factor 10 decrease in speed, and for more than 3000 RPM, recommended viscosity decreases with factor 3 for a factor 10 increase in speed.[7]

The industry standard life calculation is based upon the work of Lundberg and Palmgren performed in 1947. The formula assumes the life to be limited by metal fatigue and that the life distribution can be described by a Weibull distribution. Many variations of the formula exist that include factors for material properties, lubrication, and loading. Factoring for loading may be viewed as a tacit admission that modern materials demonstrate a different relationship between load and life than Lundberg and Palmgren determined .[7]

Jules Suriray, a Parisian bicycle mechanic, designed the first radial style ball bearing in 1869,[2] which was then fitted to the winning bicycle ridden by James Moore in the world's first bicycle road race, Paris-Rouen, in November 1869.[3]

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Bearings can withstand their maximum load only if the mating parts are properly sized. Bearing manufacturers supply tolerances for the fit of the shaft and the housing so that this can be achieved. The material and hardness may also be specified.[7]

Although bearings had been developed since ancient times, the first modern recorded patent on ball bearings was awarded to Philip Vaughan, a Welsh inventor and ironmaster who created the first design for a ball bearing in Carmarthen in 1794. His was the first modern ball-bearing design, with the ball running along a groove in the axle assembly.[1]

If an axle has two bearings, and temperature varies, axle shrinks or expands, therefore it is not admissible for both bearings to be fixed on both their sides, since expansion of axle would exert axial forces that would destroy these bearings. Therefore, at least one of the bearings must be able to slide.[7]

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Lubrication can be done with a grease, which has advantages that grease is normally held within the bearing releasing the lubricant oil as it is compressed by the balls. It provides a protective barrier for the bearing metal from the environment, but has disadvantages that this grease must be replaced periodically, and maximum load of bearing decreases (because if bearing gets too warm, grease melts and runs out of bearing). Time between grease replacements decreases very strongly with diameter of bearing: for a 40 mm bearing, grease should be replaced every 5000 working hours, while for a 100 mm bearing it should be replaced every 500 working hours.[7]

For single-row deep-groove ball bearings, SKF's documentation says that maximum axial load is circa 50% of maximum radial load, but it also says that "light" and/or "small" bearings can take axial loads that are 25% of maximum radial load.[7]

For a bearing to operate properly, it needs to be lubricated. In most cases the lubricant is based on elastohydrodynamic effect (by oil or grease) but working at extreme temperatures dry lubricated bearings are also available.

In general, maximum load on a ball bearing is proportional to outer diameter of the bearing times the width of the bearing (where width is measured in direction of axle).[7]

Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area between the balls and races. However, they can tolerate some misalignment of the inner and outer races.

Common ball bearing designs include angular contact, axial, deep-groove, and preloaded pairs. The balls in ball bearings can also be configured in various ways. Ball bearings are used in a wide range of applications, some of which include skateboards and centrifugal pumps.

Fittings that are not allowed to slip are made to diameters that prevent slipping and consequently the mating surfaces cannot be brought into position without force. For small bearings this is best done with a press because tapping with a hammer damages both bearing and shaft, while for large bearings the necessary forces are so great that there is no alternative to heating one part before fitting, so that thermal expansion allows a temporary sliding fit.[7]

Often Conrad-style ball bearings will exhibit contact ellipse truncation under axial load. That means that either the ID of the outer ring is large enough, or the OD of the inner ring is small enough, so as to reduce the area of contact between the balls and raceway. When this is the case, it can significantly increase the stresses in the bearing, often invalidating rules of thumb regarding relationships between radial and axial load capacity. With construction types other than Conrad, one can further decrease the outer ring ID and increase the inner ring OD to guard against this.

If a shaft is supported by two bearings, and the center-lines of rotation of these bearings are not the same, then large forces are exerted on the bearing, which may destroy it. Some very small amount of misalignment is acceptable, and how much depends on type of bearing. For bearings that are specifically made to be 'self-aligning', acceptable misalignment is between 1.5 and 3 degrees of arc. Bearings that are not designed to be self-aligning can accept misalignment of only 2–10 minutes of arc (0.033-0.166 degrees) .[7]

Bearingmanufacturing Machine

智通財經APP獲悉，國海證券發佈研究報告稱，維持深圳國際(00152)“買入”評級，預計2024-2026年營業收入分別為165.89億港元、172.50億港元與177.89億港元，歸母淨利潤分別為38.02億港元、38.78億港元與39.68億港元，對應股息率分別為13.22%、13.48%與13.79%。公司掌握優質資產，持續穩定高股息，未來價值迴歸路徑清晰。事件:2024年3月28日，深圳國際發佈2023年度全年業績公告：2023年，公司實現營業收入207.11億港元，同比增長32.70%，完成歸母淨利潤19.02億港元，同比增長51.66%。報告主要觀點如下：高速港口構築利潤基礎，物流園轉型升級實現歸母淨利17.46億港元2023年，公司高速及港口業務繼續貢獻穩定收益，上述板塊合計貢獻歸母淨利潤10.92億港元，為公司構築利潤基礎。由於2023年公司物流業務未有REITs項目出表，使得物流業務實現歸母淨利潤5.32億港元，同比下降62.69%。而物流園轉型升級業務則為公司業績做出較大貢獻，該板塊實現歸母淨利潤17.46億港元，主要系前海住宅項目頤城棲灣裏竣工交付，公司確認收入約55億港元，實現税後收益15.63億港元，同時，按會計準則2023年無需確認應占聯營公司深圳航空的進一步虧損，最終公司2023年完成歸母淨利潤19.02億港元，同比增長51.66%，業績符合該行預期。物流主業穩步成長，土地改性及REITs出表持續貢獻利潤彈性作為中國第八大物流地產商，截至2023底，公司物流園規劃土地面積超過1,000萬平方米，當中已獲取經營權的土地面積約908萬平方米，運營面積約476萬平方米，公司計劃到2025年底物流園投營達800萬平方米，物流業務穩步成長。與此同時，公司以“投建管轉”和“投建融管”的創新型商業模式充分挖掘物流園土地價值，土地改性及REITs出表持續貢獻利潤彈性。①投建管轉方面，“梅林關”、“前海”、“華南物流園”等地產項目逐年兑現。其中前海項目數年來已先後6次釋放税前收益合共約人民幣142.19億元，助力公司業績穩定增長。在前海項目地產開發進入尾聲之際，2023年10月底，公司旗下華南物流園土地整備正式落地，公司共獲得10.58 億元的拆遷補償費+10.87萬平方米留用土地，其中規劃可出售商品住房50.83萬平方米。根據該行測算，該項目有望為公司創造税後收益157.71億人民幣。②投建融管方面，截至2023底，深圳國際已有3個項目完成REITs出表工作，其中南昌綜合物流港確認歸母淨利潤1.75億港元；杭州項目二期和合肥肥東項目合計貢獻歸母淨利潤6.57億港元。目前公司正積極推進杭州項目一期及貴州項目的公募REITs發行工作，並已取得階段性進展。持續穩定高股息，低估值提供安全邊際公司高度重視股東回報，承諾每年核心業務利潤分派比例不低於30%，但公司實際的分紅比例常年維持在50%左右，2018-2022五年時間共計派息93.83億港元。2023年，公司擬每股派息0.40港元，股息總額為9.57億港元，分紅比例達50%。若公司繼續保持50%分紅比例，該行預計公司2024、2025年股息率分別為13.22%、13.48%；對應PE分別為3.78、3.71倍，低估值高股息資產的價值迴歸路徑清晰。

There are several common designs of ball bearing, each offering various performance trade-offs. They can be made from many different materials, including stainless steel, chrome steel, and ceramic (silicon nitride, Si3N4). A hybrid ball bearing is a bearing with ceramic balls and metal races.

The calculated life for a bearing is based on the load it carries and its operating speed. The industry standard usable bearing lifespan is inversely proportional to the bearing load cubed.[citation needed] Nominal maximum load of a bearing, is for a lifespan of 1 million rotations, which at 50 Hz (i.e., 3000 RPM) is a lifespan of 5.5 working hours. 90% of bearings of that type have at least that lifespan, and 50% of bearings have a lifespan at least 5 times as long.[7]

A 'freely sliding fit' is one where there is at least a 4 μm clearance, presumably because surface-roughness of a surface made on a lathe is normally between 1.6 and 3.2 μm.[7]

For a bearing to have its nominal lifespan at its nominal maximum load, it must be lubricated with a lubricant (oil or grease) that has at least the minimum dynamic viscosity (usually denoted with the Greek letter ν {\displaystyle \nu } ) recommended for that bearing.[7]

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If the viscosity of lubricant is higher than recommended, lifespan of bearing increases, roughly proportional to square root of viscosity. If the viscosity of the lubricant is lower than recommended, the lifespan of the bearing decreases, and by how much depends on which type of oil being used. For oils with EP ('extreme pressure') additives, the lifespan is proportional to the square root of dynamic viscosity, just as it was for too high viscosity, while for ordinary oils lifespan is proportional to the square of the viscosity if a lower-than-recommended viscosity is used.[7]

The part of a bearing that rotates (either axle hole or outer circumference) must be fixed, while for a part that does not rotate this is not necessary (so it can be allowed to slide). If a bearing is loaded axially, both sides must be fixed.[7]